hi sue have you tried https://www.thecoursemix.co.uk/courses/british-sign-language-level-3-4-course/
for both its currently £39. hopefully someone has already tried this course and has a view.
I have just started level 1 so I'm not sure if you would've covered the subjects in this 3 and 4 - the website has level 3 on its own for £19 too.
Jonny